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In the approximate interval 850–1150C, the Laves phase TiCr2 exhibits several composition dependent structures, ranging from two layer hexagonal (2H), denoted C14, to face-centered cubic, denoted C15, for Ti-deficient and Ti-excess material, respectively. Intermediate stacking variants such a dihexagonal (4H), denoted C36, may also exist. The Laves phase band in a Ti-Cr microdiffusion couple is examined in cross-section TEM at ambient temperature, after a 1000 C anneal. The band consists of very faulty hexagonal material, at least in part reflecting rapid shear transformation on cooling; in addition the cubic phase is present, in some instances within the same grain as the hexagonal phase. The cubic/hexagonal interfaces are approximately parallel rather than perpendicular to the bulk diffusion direction. Due to a difference in Ti and Cr fluxes, there is a gradual transformation of cubic to hexagonal by a shear mechanism. A model for the mobility of the hexagonal/cubic interface in a concentration gradient is proposed.

Mg is the most important lightweight engineering alloy enabling future weight-reduced and fuel-saving engineering solutions. Yet, Mg is soft. Long-period stacking ordered (LPSO) structures in Mg alloys have unique crystal structures, characterized by both complex chemical and stacking order. They are essential for strengthening of Mg alloys. The formation mechanism of these LPSO structures is still under discussion. Here we report that Y/Zn enriched Guinier-Preston (GP) zones observed in a lean Mg-Y-Zn model alloy are precursors of early stage LPSO structures. We provide evidence of a new type of phase transformation mechanism which comprises the diffusional formation of Y/Zn enriched GP zones and their subsequent shear transformation into LPSO building blocks. The mechanism constitutes a new type of coupled diffusional-displacive phase formation sequence which may also be applicable to other alloy systems.

In this work, structural and mechanical properties of hydrogen-charged metallic glass are studied to evaluate the effect of hydrogen on early plasticity. Hydrogen is introduced into samples of a Zr-based (Vit 105) metallic glass using electrochemical charging. Nanoindentation tests reveal a clear increase in modulus and hardness as well as in the load of the first pop-in with increasing hydrogen content. At the same time, the probability of a pop-in occurring decreases, indicating that hydrogen hinders the onset of plastic instabilities while allowing local homogeneous deformation. The hydrogen-induced stiffening and hardening is rationalized by hydrogen stabilization of shear transformation zones (STZs) in the amorphous structure, while the improved ductility is attributed to the change in the spatial correlation of the STZs.

Controlling shear band propagation is the key to obtain ductile metallic glasses. Here, we use a residual stress field to vary the direction of shear band propagation. We ascribe this behavior to the effect of the stress field on the activation of shear transformation zones (STZs) along their characteristic direction and we quantify this contribution to the energy of the process. Because of the progressively adverse orientation of the stress field, the energy stored as shear in the STZ decreases to a level where shear band propagation at alternative angles becomes energetically more favorable.

The lattice transformations by which ferromagnetic AlMn(C) is formed have been studied by transmission electron microscopy and diffraction. After an initial ordering transition, further transformation takes place by a shear mechanism. The ordering in the close packed planes is preserved throughout the shear transformation.

For an N-generation Kobayashi-Maskawa mixing matrix having the property that matrix elements decrease rapidly with increasing generation change, we show by construction that knowledge of the moduli of all elements is sufficient, up to a discrete ambiguity, to determine all phase information.

Two mechanisms were proposed to explain the decomposition reaction of brucite: the homogeneous and the inhomogeneous mechanisms. These two mechanisms, on the one hand, and the main structural transformation modes, on the other, are reviewed and discussed in connection with an important new result. When no sintering occurs the oxide crystallite size is independent of temperature, i.e. it is independent of the overall reaction rate. This result excludes a diffusion process and is in agreement with the homogeneous mechanism.It is shown that the structural transformation associated with this reaction exhibits the most important morphological and structural features of a shear transformation.